Single- or dual-fuel engines that use a gaseous fuel are known and used for various applications, such as generator sets, engine-driven compressors, engine driven pumps, machines, on- and off-highway trucks, and others. The operation of such engines by substitution of a certain amount of heavy fuel, such as diesel, with a lighter fuel, such as natural gas, biogas, liquid petroleum gas (LPG) or other types of fuel that may be more readily available and cost effective, makes them more effective to operate. In some applications, the gas engines may be operating entirely on the gaseous fuel.
Unlike liquid fuels such as gasoline or diesel, which are provided to the engine at a high pressure and are typically directly injected into the engine cylinders for modern engines, gaseous fuels can be provided to the engine at relatively lower pressures and are injected or fumigated into an air stream that is provided to the engine cylinder(s). For controlling engine emissions and power, it is important to provide the engine cylinders with a relatively homogeneous fuel/air mixture, which requires sufficient time for the fuel to mix with the air after injection. However, the engine response to fuelling changes, for example, during transient engine operation, is improved if the time available for fuel/air mixing is reduced. Moreover, different engine applications having common intake air hardware but different operating flows and fueling rates cannot exploit the same gas diffusion structures.
In a previously proposed method of improving mixing of a gaseous fuel in an engine intake air stream as shown, for example, in WO 1998/059165 A1 (“Zilocchi”), it was proposed to include a structure in which the air/fuel ratio for various engines may be adjusted using the same structure. In Zilocchi, the adjustment of the air/fuel ratio is accomplished by adjusting the relative position and/or orientation of moveable and cooperating components presenting different gas and air flow areas. However, systems such as Zilocchi's are only partially effective in addressing variability between different engine applications and may also increase pressure drop for air and gas being provided to the engine, this increasing pumping losses of the engine and decreasing efficiency.